diff --git a/ChangeLog b/ChangeLog
index a3516edd42..acf01fb034 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Fri May 21 12:25:58 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* marshal.c (w_float): use dtoa directly instead of stripping
+	  needless trailing .0.
+
+	* numeric.c (flo_to_s): reverted.  [ruby-dev:41341]
+
 Fri May 21 01:06:05 2010  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* thread.c (subtract_tv): if the rest is zero, should finish waiting
diff --git a/marshal.c b/marshal.c
index 583b1c9152..0339e21f4c 100644
--- a/marshal.c
+++ b/marshal.c
@@ -354,7 +354,7 @@ load_mantissa(double d, const char *buf, long len)
 static void
 w_float(double d, struct dump_arg *arg)
 {
-    int ruby_dbl2cstr(double value, char *buf, int size);
+    char *ruby_dtoa(double d_, int mode, int ndigits, int *decpt, int *sign, char **rve);
     char buf[FLOAT_DIG + (DECIMAL_MANT + 7) / 8 + 10];
 
     if (isinf(d)) {
@@ -369,9 +369,37 @@ w_float(double d, struct dump_arg *arg)
 	else           w_cstr("0", arg);
     }
     else {
-	int len = ruby_dbl2cstr(d, buf, (int)sizeof(buf));
-	if (len > 2 && buf[len - 1] == '0' && buf[len - 2] == '.')
-	    len -= 2;
+	int decpt, sign, digs, len = 0;
+	char *e, *p = ruby_dtoa(d, 0, 0, &decpt, &sign, &e);
+	if (sign) buf[len++] = '-';
+	digs = (int)(e - p);
+	if (decpt < -3 || decpt > digs) {
+	    buf[len++] = p[0];
+	    buf[len++] = '.';
+	    memcpy(buf + len, p + 1, --digs);
+	    len += digs;
+	    len += snprintf(buf + len, sizeof(buf) - len, "e%d", decpt - 1);
+	}
+	else if (decpt > 0) {
+	    memcpy(buf + len, p, decpt);
+	    len += decpt;
+	    if ((digs -= decpt) > 0) {
+		buf[len++] = '.';
+		memcpy(buf + len, p + decpt, digs);
+		len += digs;
+	    }
+	}
+	else {
+	    buf[len++] = '0';
+	    buf[len++] = '.';
+	    if (decpt) {
+		memset(buf + len, '0', -decpt);
+		len -= decpt;
+	    }
+	    memcpy(buf + len, p, digs);
+	    len += digs;
+	}
+	xfree(p);
 	w_bytes(buf, len, arg);
     }
 }
diff --git a/numeric.c b/numeric.c
index fec4794330..ef9bdce489 100644
--- a/numeric.c
+++ b/numeric.c
@@ -545,8 +545,6 @@ rb_float_new(double d)
     return (VALUE)flt;
 }
 
-int ruby_dbl2cstr(double value, char *buf, int size);
-
 /*
  *  call-seq:
  *     flt.to_s  ->  string
@@ -560,70 +558,70 @@ int ruby_dbl2cstr(double value, char *buf, int size);
 static VALUE
 flo_to_s(VALUE flt)
 {
+    char *ruby_dtoa(double d_, int mode, int ndigits, int *decpt, int *sign, char **rve);
     enum {decimal_mant = DBL_MANT_DIG-DBL_DIG};
     enum {float_dig = DBL_DIG+1};
     char buf[float_dig + (decimal_mant + CHAR_BIT - 1) / CHAR_BIT + 10];
     double value = RFLOAT_VALUE(flt);
+    VALUE s;
+    char *p, *e;
+    int sign, decpt, digs;
 
     if (isinf(value))
 	return rb_usascii_str_new2(value < 0 ? "-Infinity" : "Infinity");
     else if (isnan(value))
 	return rb_usascii_str_new2("NaN");
-    return rb_usascii_str_new(buf, ruby_dbl2cstr(value, buf, (int)sizeof(buf)));
-}
 
-int
-ruby_dbl2cstr(double value, char *buf, int size)
-{
-    char *ruby_dtoa(double d_, int mode, int ndigits, int *decpt, int *sign, char **rve);
-    char *p, *e;
-    int sign, decpt, digs;
-
-    if (size <= 0) return 0;
     p = ruby_dtoa(value, 0, 0, &decpt, &sign, &e);
-    if (sign) *buf++ = '-', --size;
-    if ((digs = (int)(e - p)) >= size) digs = size - 1;
-    if (decpt > -4 && (decpt < digs || decpt - digs < DBL_DIG+1)) {
-	int i = 0, j = 0, n;
-	if (decpt > 0) {
-	    memcpy(buf + j, p + i, (n = decpt > digs ? digs : decpt));
-	    i += n, j += n;
-	    if ((n = decpt - n) > 0) {
-		memset(buf + j, '0', n);
-		j += n;
-	    }
-	}
-	else {
-	    buf[j++] = '0';
-	}
-	buf[j++] = '.';
-	if (decpt < 0) {
-	    memset(buf + j, '0', -decpt);
-	    j -= decpt, decpt = 0;
-	}
+    s = sign ? rb_usascii_str_new_cstr("-") : rb_usascii_str_new(0, 0);
+    if ((digs = (int)(e - p)) >= (int)sizeof(buf)) digs = (int)sizeof(buf) - 1;
+    memcpy(buf, p, digs);
+    xfree(p);
+    if (decpt > 0) {
 	if (decpt < digs) {
-	    memcpy(buf + j, p + i, (n = digs - decpt));
-	    j += n;
+	    memmove(buf + decpt + 1, buf + decpt, digs - decpt);
+	    buf[decpt] = '.';
+	    rb_str_cat(s, buf, digs + 1);
+	}
+	else if (decpt - digs < float_dig) {
+	    long len;
+	    char *ptr;
+	    rb_str_cat(s, buf, digs);
+	    rb_str_resize(s, (len = RSTRING_LEN(s)) + decpt - digs + 2);
+	    ptr = RSTRING_PTR(s) + len;
+	    if (decpt > digs) {
+		memset(ptr, '0', decpt - digs);
+		ptr += decpt - digs;
+	    }
+	    memcpy(ptr, ".0", 2);
 	}
 	else {
-	    buf[j++] = '0';
+	    goto exp;
 	}
-	digs = j;
+    }
+    else if (decpt > -4) {
+	long len;
+	char *ptr;
+	rb_str_cat(s, "0.", 2);
+	rb_str_resize(s, (len = RSTRING_LEN(s)) - decpt + digs);
+	ptr = RSTRING_PTR(s);
+	memset(ptr += len, '0', -decpt);
+	memcpy(ptr -= decpt, buf, digs);
     }
     else {
-	buf[0] = p[0];
-	buf[1] = '.';
+      exp:
 	if (digs > 1) {
-	    memcpy(buf + 2, p + 1, digs++ - 1);
+	    memmove(buf + 2, buf + 1, digs - 1);
 	}
 	else {
 	    buf[2] = '0';
-	    digs = 3;
+	    digs++;
 	}
-	digs += snprintf(buf + digs, size - digs, "e%+03d", decpt - 1);
+	buf[1] = '.';
+	rb_str_cat(s, buf, digs + 1);
+	rb_str_catf(s, "e%+03d", decpt - 1);
     }
-    xfree(p);
-    return digs + sign;
+    return s;
 }
 
 /*